Folding tools such as knives have a handle with opposed halves that are held apart to define a blade-receiving space. A blade is pivotally attached to the handle with a pivot shaft or axle that has its opposite ends secured to the opposite handle halves, and which extends through a bore in the blade. The pivot shaft defines a strong and secure connection between the blade and the handle about which the blade may be pivoted between a closed position in which the blade is stowed safely in the handle, and an open position in which the blade extends away from the handle for normal use.
Although there are many different kinds of structures used for pivot shafts used to attach knife blades to knife handles, an inherent problem with pivoting knives (and other folding tools) is that there is almost always a certain amount of play between the blade and the handle. Thus, in order to enable the blade to pivot freely about the pivot shaft, there must be some tolerance between the outer diameter of the pivot shaft and the inner diameter of the bore in the blade through which the shaft extends. In high quality knives the amount of clearance between the blade bore and the shaft can be minimized, but there still must be enough tolerance to allow the blade to be pivoted relatively easily. This necessary tolerance results in rotational movement of the blade, which is perceived as wobble between the blade and the handle: this phenomena is often colloquially referred to as “tip wobble.”
Tip wobble is undesirable because it necessarily reduces the strength of the blade/handle connection. In extreme cases, tip wobble can result in an unsafe tool—this is sometimes a concern with lower quality folding knives. But tip wobble is often present even in the most highly engineered and expensive folding knives and can be both a bother and a structural limitation.
There are several common techniques utilized to eliminate, or at least minimize the amount of tip wobble. The most common approach is simply to reduce the tolerance between the blade bore and the pivot shaft—the closer the tolerance between the pivot shaft and the bore, the lesser the tip is able to wobble. The trade off with this approach is of course that a certain amount of spacing between the blade and the shaft is necessary to allow the blade to pivot freely. With automatic or semi-automatic style knives, an easily pivoting blade is a necessity. As such, this approach has its limitations. Another approach is to add a low-friction bushing around the pivot shaft so that the shaft—bore tolerance may be minimized. As with the other techniques just described, this is an effective way to help minimize tip wobble, but it does not eliminate wobble. Moreover, the bushings tend to wear and degrade over time and as they do so, tip wobble tends to increase.
Another solution relies upon a blade-locking mechanism to minimize relative movement between the blade and handle Some locking mechanisms utilize a 3 point-of-contact lock that forces out the play in the pivot bore. While this technique does help minimize blade movement, not all knife designs can incorporate these kinds of locking mechanisms. Other common locking mechanisms do not alleviate tip wobble.
There is an ongoing need therefore for manufacturing techniques and methods that reduce tip wobble in folding tools such as knives.
The present invention relates to an apparatus and method for establishing a strong, secure interconnection between a folding tool implement and the handle of the folding tool, and which minimizes or eliminates tip wobble while insuring that the implement may be easily pivoted between the open and closed positions. The invention allows the diameter of the pivot shaft to be varied, thereby allowing the diameter of the shaft to be effectively increased so that the shaft extends to and makes contact with the interior surface of the bore through the blade, without restricting the ability of the blade to freely rotate about the shaft.